The improvement involves the use of a simplified mechanism for preventing the contamination of an endless ribbon by the lubricating oils on the print wires of a wire matrix printer.
The problem solved by this invention is the result of a unique set of circumstances. In order to print rapidly with a wire matrix printer, it is necessary to move the wires very short distances, i.e., in the order of 0.020 inches to 0.030 inches. This means that the ribbon must lie in a very short gap between the ends of the print wires and the document forms being printed on. In addition, the print wires are held within and are guided by a member that must position them accurately for the life of the printer. In order to prevent undue wear of the wires and guide member, it is necessary to provide lubrication in guide member openings through which the print wires are moved to engage the ribbon. Preferably the ribbon is held against the guide member and the ends of the print wires.
When the printer sits idle for an extended period of time such as a few hours, oil from the lubricating system can find its way from the print wires and guide member to the ribbon and cause a portion of the ribbon to be wetted. The oily portion of the ribbon can cause the printing to be either too light or too dark. The problem, therefore, is to find some inexpensive reliable means of keeping the ribbon free of oil when it is not in use for a number of hours.
At least one prior known solution suggested for this problem involved supporting the ribbon continuously at a short distance from the tip of the print head so that it could not become contaminated. This solution has been found to be marginal and small adjustments must be made periodically to assure the maintenance of a suitable gap at all times. In at least one known implementation of such an arrangement, the means for maintaining the ribbon away from the print head wire aperatures has been known to result in the accumulation of contaminating substances in the vicinity of the wire aperatures causing undersirable smudging on the documents. Also a wider gap is required between the guide member/print wires and the documents being printed on.
It is, therefore, a primary object of the present invention to provide an improved means for preventing the contamination of ribbons.